Conventional tool exchangers in press brakes are disclosed by, for example, Unexamined Japanese Patent Application KOKAI (laid open) Publication No. H9-85849, Unexamined Japanese Patent Application KOKAI (laid open) Publication No. 2001-150032, and PCT International Publication No. WO00/41824.
Among those exchangers, one disclosed by Unexamined Japanese Patent Application KOKAI (laid open) Publication No. H9-85349 is provided with a plurality of center tools whose lengths are increased by, for example, 5 mm pitch per tool and which is housed in a tool cartridge on the center of an upper table (for example, FIG. 2 of this publication).
According to this structure, as a center tool with a predetermined length is selected from the tool cartridge, and split tools slidable rightward and leftward are gathered in the center tool, a process station which has a tool layout with a predetermined length is built.
The tool exchanger of the Unexamined Japanese Patent Application KOKAI (laid open) Publication No. 2001-150032 provides tool racks on both sides of a press brake main body (for example, FIG. 1 of this publication), and one tool rack houses a tool group undergone layout beforehand.
According to this structure, after a process is finished, a used tool is removed from the press brake main body and transferred to the other tool rack, and the tool group undergone layout as explained above is transferred from one tool rack to the press brake main body and attached to it.
The tool exchanger of PCT International Publication No. WO00/41824 is provided with a cartridge which houses split tools of different lengths on one side of a press brake main body (for example, FIG. 23 of this publication).
According to this structure, a tool group which combines tools of various lengths are automatically made, transferred to the press brake main body each making, and a process station with a predetermined tool layout is built.
The tool exchanger of Unexamined Japanese Patent Application KOKAI (laid open) Publication No. H9-85349 has the single process station, and is suitable for a center bend process which performs process at the center of the upper and lower tables, but may not accept step bending.
That is, as illustrated in FIG. 33 of this application, in the case of step bending in which a workpiece W is transferred to a plurality of different process stations st1, st2, st3 with respect to each bending order to do process, such step bending may not be acceptable if the tool cartridge at the center of the upper table shown by Unexamined Japanese Patent Application KOKAI (laid open) Publication No. H9-85349 houses plenty kinds of center tools.
Because the tool exchanger of Unexamined Japanese Patent Application KOKAI (laid open) Publication No. 2001-150032 is, as explained above, provided with the tool racks on both sides of the press brake main body, the press brake becomes wide transversally by just that much, and an extra housing space becomes necessary, and a worker may insert an incorrect-layout tool group into one mold rack, and in this case, a desired bending becomes impossible, and a process efficiency is remarkably decreased.
Further, as explained above, the tool exchanger of PCT International Publication No. WO00/41824 combines split tools of different lengths, and builds a plurality of process stations, but in a case where the number of tools of the same length is insufficient, step bending may not be carried out easily and rapidly.
For example, as illustrated in FIG. 34 of this application, in a case where four tools pA, dA with lengths of 10 mm are required at a process station stA but one of them is lacked and there is no spare in the housing cartridge, after a process at a process station stB is finished, tool pB, dB used at the process station stB with lengths of 10 mm should be transferred to the process station stA to do process.
Moreover, because PCT International Publication No. WO00/41824 creates a tool layout with reference to the length of the tool (FIG. 46 of this publication), it requires complex calculation, and also requires a lot of time for tool-layout creation, and it cannot rapidly cope with step bending.
In Japanese Patent Application No. 2008-177586 (filed in June 23, Heisei 15) which is the basic application of this application, a tool group is constituted by split tools with the same length, and a plurality of process stations are formed to cope with a predetermined bending length, but in this method, in a case where the lengths of the process stations are longer than or equal to a certain length, the number of tools becomes large, a lots of scratches are formed on a workpiece among the individual split tools, and particularly, this becomes a problem for a product which requires an appearance quality.
To overcome this problem, process is carried out with a film-like scratch prevention sheet being attached to the surface of a workpiece, but it requires attachment and removal of the sheet before and after the process, and this causes increment of entire process time, resulting in being unable to cope with step bending easily and rapidly, reducing a process efficiency, and increment of a coat.
The object of the invention is to improve a process efficiency and save a tool-housing space in a bending apparatus by coping with step bending easily and rapidly.